Most of the monoclonal antibodies currently employed in the development of antibody pharmaceuticals are humanized mouse antibodies. That is because the mouse hybridoma method has been established as a method of producing monoclonal antibodies. However, many of the functional antigen epitopes of human proteins that are used as antibody drug markers have a high degree of homology with the amino acid sequences of both humans and mice. Even when mice are immunized to such antigens, it is difficult to obtain highly specific antibodies due to immune tolerance. Thus, it is necessary to fabricate a large number of hybridomas and screen them in order to obtain antibodies of high capability. Accordingly, there is a need to develop a means of efficiently producing monoclonal antibodies of high capability by inducing immunization in animal species having amino acid sequences that differ as much as possible from human antigens and avoiding the limits of immune tolerance to develop new antibody pharmaceuticals.
In the conventional fabrication of monoclonal antibodies, the method of fusing antibody-producing cells with myeloma cells to fabricate hybridomas having autonomous replication capability and screening those clones having the ability to produce antibodies that are specific to the target from among them has been widely employed. However, there are a number of drawbacks to the hybridoma method. For one, the hybridoma technique is limited to mouse antibody-producing cells, and is difficult to apply to other animal species. There is a further drawback in that time and effort are required to clone hybridomas. Moreover, there is a problem in that even when screening is conducted, there is no guarantee of obtaining clones having the ability to produce antigen specific antibodies.
To overcome these drawbacks, the method of identifying plasma cells (antigen specific plasma cells) having the ability to produce antigen specific antibodies by applying the ELISPOT method has been developed to fabricate human monoclonal antibodies (Japanese Examined Patent Publication (KOKOKU) No. 2009-34047: Patent Reference 1 (WO2009/017226, US2011/0294678A1 (which are hereby included in their entirety by reference)). It is a method by which plasma cells purified from human lymphocytes are introduced into microcells that have been specially processed, antibodies that are secreted in large quantities by the plasma cells are immobilized on the base surrounding the plasma cells, labeled antigen is reacted therewith, and antigen specific plasma cells are identified.